Rotor casing of screw compressor, and screw compressor

Abstract

To reduce friction resistance such as sliding loss between a screw rotor of a screw compressor and the inner wall face of a rotor casing, and also reduce undesired contact therebetween.SOLUTION: The rotor casing of the screw compressor in at least one embodiment of this invention includes a first rotor casing and a second rotor casing split on a split surface parallel to the virtual flat surface including a virtual center axis of a male rotor and a virtual center axis of a female rotor, the first rotor casing and the second rotor casing each having an inner wall face forming a closed space to compress compressed gas sucked from a suction port on one side in the axial direction of the screw rotor, the second rotor casing being communicated with a discharge port on the other side in the axial direction. In at least part of region in the axial direction, the curvature radius of the inner wall face of the first rotor casing is larger than the curvature radius of the inner wall face of the second rotor casing.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a rotor casing for a screw compressor and a screw compressor. [Background technology]

[0002] A screw compressor includes a screw rotor including a pair of male and female rotors, and a rotor casing that houses the screw rotor (see, for example, Patent Document 1). Screw compressors have excellent advantages such as a simple structure and good durability, and are therefore widely used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 100911 Summary of the Invention [Problem to be solved by the invention]

[0004] In a screw compressor, frictional resistance such as sliding loss occurs between the tooth tips and the inner wall surface of the rotor casing when the screw rotor rotates. Also, in a screw compressor, the pressures in the multiple confined spaces created by the meshing of the teeth are different, so the entire shaft of the screw rotor is pushed toward the side with the lower pressure. However, because both ends of the screw rotor are supported by radial bearings, the area where the teeth are provided is displaced in an arched shape, which can lead to undesired contact between the screw rotor and the inner wall surface of the rotor casing. Furthermore, the pressure in the confined spaces in the axial direction of the screw rotor is higher on the discharge side than on the suction side, and due to the twisted shape of the screw rotor, the pressure in each tooth groove (each confined space) differs even in a cross section with the same axial position. Due to the relationship between this difference in pressure in each tooth groove and the support position of the screw rotor, the position where the bow-shaped deformation in the region where the teeth of the screw rotor are provided is greatest is a position shifted toward the discharge side from the axial center position of the region where the teeth are provided.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to reduce frictional resistance such as sliding loss between the tooth tips of a screw rotor and the inner wall surface of a rotor casing in a screw compressor, and to reduce undesired contact between the screw rotor and the inner wall surface of the rotor casing. [Means for solving the problem]

[0006] (1) A rotor casing of a screw compressor according to at least one embodiment of the present disclosure includes: A rotor casing for a screw compressor that houses a screw rotor including a pair of male and female rotors, the rotor casing includes a first rotor casing and a second rotor casing divided by a dividing plane parallel to an imaginary plane including an imaginary central axis of the male rotor and an imaginary central axis of the female rotor, the first rotor casing and the second rotor casing have inner wall surfaces that form a confined space for compressing the gas to be compressed that is sucked in from a suction port on one side in the axial direction of the screw rotor, the second rotor casing communicates with a discharge port on the other side in the axial direction, In at least a portion of the axial region, the radius of curvature of the inner wall surface of the first rotor casing is larger than the radius of curvature of the inner wall surface of the second rotor casing.

[0007] (2) A screw compressor according to at least one embodiment of the present disclosure includes: a screw rotor including a pair of male and female rotors; A rotor casing of the screw compressor having the configuration (1) above; Equipped with. [Effects of the Invention]

[0008] According to at least one embodiment of the present disclosure, it is possible to reduce frictional resistance such as sliding loss between the tooth tips of the screw rotor and the inner wall surface of the rotor casing in a screw compressor, and to reduce undesired contact between the screw rotor and the inner wall surface of the rotor casing. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional plan view of a screw compressor according to some embodiments. FIG. [Figure 2] FIG. 2 is a schematic perspective view of a rotor casing of a screw compressor according to some embodiments. [Figure 3] FIG. 2 is a schematic diagram illustrating a rotor casing of a screw compressor according to some embodiments, viewed from the axial direction of the screw rotor. [Figure 4] 4 is a cross section taken along line IV-IV in FIG. 3. [Figure 5] 4 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. 3. FIG. [Figure 6] 4 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. 3. FIG. [Figure 7] 4 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. 3. FIG. [Figure 8] 4 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. 3. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0011] (Screw compressor configuration) Fig. 1 is a schematic cross-sectional plan view of a screw compressor according to some embodiments. As shown in Fig. 1, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) including a pair of rotor shafts 14, 16, and a rotor casing 12 that houses the pair of screw rotors.

[0012] FIG. 2 is a schematic perspective view of a rotor casing of a screw compressor according to some embodiments. FIG. 3 is a schematic view of a rotor casing of a screw compressor according to some embodiments, as viewed from the axial direction of the screw rotor. In the screw compressor 2 according to some embodiments, the rotor casing 12 includes a first rotor casing 121 and a second rotor casing 122 divided by a dividing plane Pd parallel to an imaginary plane Pv including the imaginary central axis of the male rotor 15 (i.e., the central axis AX1 of the rotor shaft 14 when the male rotor 15 is disposed in the rotor casing 12 shown in Figures 2 and 3) and the imaginary central axis of the female rotor 17 (i.e., the central axis AX2 of the rotor shaft 16 when the female rotor 17 is disposed in the rotor casing 12 shown in Figures 2 and 3). In the example shown in FIGS. 2 and 3, the dividing plane Pd coincides with the virtual plane Pv.

[0013] The pair of rotor shafts 14, 16 are supported by a radial bearing 18 and a thrust bearing 20 so as to be rotatable about central axes AX1, AX2 of the rotor shafts 14, 16, respectively. In the following description, the direction along the central axes AX1, AX2 will be referred to as the axial direction of the screw rotor, or simply as the axial direction; the radial direction centered on the central axes AX1, AX2 will also be referred to as the radial direction of the male rotor 15, the radial direction of the female rotor 17, or simply as the radial direction; and the circumferential direction centered on the central axes AX1, AX2 will also be referred to as the circumferential direction of the male rotor 15, the circumferential direction of the female rotor 17, or simply as the circumferential direction.

[0014] In the screw compressor 2 according to some embodiments, the suction-side radial bearing 18 among the radial bearings 18 is held in a suction-side bearing housing 21. In the screw compressor 2 according to some embodiments, the suction-side bearing housing 21 is coupled to the suction-side end of the rotor casing 12. In the screw compressor 2 according to some embodiments, the radial bearing 18 on the discharge side of the radial bearings 18 and the thrust bearing 20 are held in a discharge-side bearing housing 22. In the screw compressor 2 according to some embodiments, the discharge-side bearing housing 22 is coupled to the end of the rotor casing 12 on the discharge side. The radial bearing 18 may be, for example, a sliding bearing or a rolling bearing.

[0015] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. The meshing of the teeth of the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12 form a plurality of tooth groove spaces along the axial direction of the rotor shafts 14, 16.

[0016] The rotor shaft 14 that constitutes the male rotor 15 is connected to the output shaft of a motor (not shown), and the male rotor 15 is configured to be driven to rotate by the motor in the direction indicated by arrow a in Figures 1 and 3. The female rotor 17 that meshes with the male rotor 15 rotates in the opposite direction to the rotation of the male rotor 15, as indicated by arrow b in Figures 1 and 3. When the male rotor 15 and female rotor 17 rotate in their meshed state, the tooth groove spaces move axially from the suction side to the discharge side.

[0017] The tooth groove space described above receives compressed gas from an intake space 50 formed in the rotor casing 12 via an intake port 52. When the male rotor 15 and the female rotor 17 rotate, the tooth groove space moves axially from the intake side to the discharge side in accordance with the rotation of these screw rotors. During this process, the intake port 52 is closed, and the tooth groove space becomes a sealed confined space. The volume of the confined space decreases as the screw rotor rotates, compressing the compressed gas in the confined space. When the confined space reaches the discharge port 54 and communicates with a discharge space (not shown) formed in the rotor casing 12, the compressed gas in the confined space is discharged to the discharge space. The intake port 52 is located at one axial end (intake side) of the rotor casing 12. The discharge port 54 is formed by an opening (not shown) located in the end face of the second rotor casing 122 on the other axial end (discharge side) in the axial direction.

[0018] An expanded diameter portion 12a is provided on the suction side inner wall surface 12W of the rotor casing 12. The expanded diameter portion 12a is in communication with the suction port 52 and connects adjacent tooth groove spaces in the axial direction. The expanded diameter portion 12a has an inner diameter larger than that of the compression section inner wall surface 12Wp, which is the inner wall surface 12W that forms the confinement space. As the screw rotor rotates, the tooth groove spaces move axially from the suction side to the discharge side, and the compressed gas flows into tooth groove spaces that were not able to sufficiently suck in the compressed gas via the expanded diameter portion 12a. As described above, the inner diameter of the enlarged diameter portion 12a is set to a degree that allows the compressed gas to flow between adjacent tooth groove spaces via the enlarged diameter portion 12a. On the other hand, the inner diameter of the compression portion inner wall surface 12Wp is set to minimize leakage of the compressed gas from the tooth groove spaces. The enclosed space is isolated from the enlarged diameter portion 12a.

[0019] FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. FIG. 6 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. FIG. 7 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG. FIG. 8 is a cross-sectional view of another rotor casing, corresponding to the cross section taken along the line IV-IV in FIG.

[0020] (Regarding the inner wall surface 12W of the first rotor casing 121) In general, in a screw compressor, frictional resistance such as sliding loss occurs between the tooth tips and the inner wall surface of the rotor casing when the screw rotor rotates. Furthermore, in general, in screw compressors, the pressures in the multiple enclosed spaces created by the meshing of the teeth are different, so the entire shaft of the screw rotor is pushed in the direction of the lower pressure. However, because both ends of the screw rotor are supported by radial bearings, the area where the teeth are provided is displaced in an arched shape, which may result in undesired contact between the screw rotor and the inner wall surface of the rotor casing. After careful consideration, the inventors found that such deformation of the screw rotor could result in increased frictional resistance, such as sliding loss, between the tips of the screw rotor teeth and the inner wall surface of the rotor casing, and that the risk of undesired contact between the screw rotor and the inner wall surface of the rotor casing was higher in the first rotor casing 121 than in the second rotor casing 122, which has a discharge port 54.

[0021] Therefore, in the screw compressor 2 according to some embodiments, the first rotor casing 121 and the second rotor casing 122 are formed so that in at least a portion of the axial direction, the radius of curvature of the compression section inner wall surface 12Wp, which is the inner wall surface 12W that forms the confined space of the first rotor casing 121, is larger than the radius of curvature of the compression section inner wall surface 12Wp of the second rotor casing 122. In addition, in the region where the radius of curvature of the compression section inner wall surface 12Wp of the first rotor casing 121 is larger than the radius of curvature of the compression section inner wall surface 12Wp of the second rotor casing 122, the difference between the radius of curvature of the compression section inner wall surface 12Wp of the first rotor casing 121 and the radius of curvature of the compression section inner wall surface 12Wp of the second rotor casing 122 is small, and it is not intended to actively leak compressed gas from the tooth groove space along the compression section inner wall surface 12Wp of the first rotor casing 121.

[0022] As a result, in the screw compressor 2 according to some embodiments, frictional resistance such as sliding loss between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the male rotor 15 and the female rotor 17 can be reduced. Furthermore, undesired contact between the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12 can be reduced. In the screw compressor 2 according to some embodiments, the gaps between the inner wall surface 12W of the second rotor casing 122 and the tooth tips of the male rotor 15 and the female rotor 17, which closely contribute to the process of compressing the gas to be compressed, can be made relatively small, thereby reducing leakage of the gas to be compressed from the gaps. That is, in the screw compressor 2 according to some embodiments, the gaps between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the male rotor 15 and the female rotor 17, and the gaps between the inner wall surface 12W of the second rotor casing 122 and the tooth tips of the male rotor 15 and the female rotor 17 can be set individually, thereby reducing frictional resistance such as sliding loss between the tooth tips of the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the first rotor casing 121, reducing undesired contact between the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12, and reducing leakage of compressed gas from the gaps between the inner wall surface 12W of the rotor casing 12 and the tooth tips of the male rotor 15 and the female rotor 17.

[0023] In some embodiments of the screw compressor 2, the region 31 in which the radius of curvature of the compression section inner wall surface 12Wp of the first rotor casing 121 is larger than the radius of curvature of the compression section inner wall surface 12Wp of the second rotor casing 122 may be the entire axial direction of the compression section inner wall surface 12Wp of the first rotor casing 121, excluding the above-mentioned expanded diameter portion 12a, as shown in Figures 4 and 7, for example. Furthermore, the region 31 may be formed at a position shifted toward the discharge side from the axial center position Cr of the rotor casing 12 (i.e., the axial center position of the portion where the spiral teeth are formed on the male rotor 15 and the female rotor 17), as shown in, for example, Figures 5, 6 and 8. The region 31 may be provided, for example, as shown in Figures 5 and 8, from a position shifted toward the discharge side from the axial center position Cr of the rotor casing 12 to the axial discharge side end 12e (see Figure 1) of the compression section inner wall surface 12Wp. The region 31 may be provided in a part of the region on the discharge side of the center position Cr in the axial direction of the rotor casing 12, for example, as shown in FIG.

[0024] (Regarding flank 30) The region 31 where the radius of curvature of the compression section inner wall surface 12Wp of the first rotor casing 121 is larger than the radius of curvature of the compression section inner wall surface 12Wp of the second rotor casing 122 may have a flank 30 defined by a curve when viewed from the axial direction. The flank 30 is preferably located radially outward of an imaginary cylindrical surface 25 whose radius is the radius of curvature of the inner wall surface 12W of the second rotor casing 122. The compression portion inner wall surface 12Wp of the first rotor casing 121 in the region 31 described above is also the clearance surface 30, and the compression portion inner wall surface 12Wp of the first rotor casing 121 in the region 31 is also referred to as the first clearance surface 30A. The above-mentioned imaginary cylindrical surface 25 is an imaginary cylindrical surface obtained when it is assumed that the compression section inner wall surface 12Wp of the second rotor casing 122 is extended in the circumferential direction.

[0025] 7 and 8, a flank 30 positioned further radially outward than the first flank 30A may be provided in a part of the axial direction in the region 31. The flank 30 positioned further radially outward than the first flank 30A is also referred to as a second flank 30B to distinguish it from the above-mentioned first flank 30A. The second flank surface 30B may extend not only to the first rotor casing 121 but also to a part of the second rotor casing 122 along the circumferential direction as shown in FIGS. By providing the second flank surface 30B, undesired contact between the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12 can be further reduced. In the following description, when there is no particular distinction between the first flank 30A and the second flank 30B or when the first flank 30A and the second flank 30B are referred to collectively, they will be simply referred to as flank 30.

[0026] Therefore, in the screw compressor 2 according to some embodiments, the provision of the relief surfaces 30 can reduce undesired contact between the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12.

[0027] In the screw compressor 2 according to some embodiments, as shown in Figures 4 to 8, the flank 30 is preferably formed at a position shifted toward the discharge side from the center position Cr in the axial direction of the rotor casing 12. In particular, when the second flank 30B is provided as shown in Figures 7 and 8, the second flank 30B is preferably formed at a position shifted toward the discharge side from the center position Cr in the axial direction of the rotor casing 12. As a result of careful investigation by the inventors, it was found that the position at which the amount of radially outward deformation when the male rotor 15 and the female rotor 17 are deformed into a bow shape is greatest is a position shifted toward the discharge side from the axial center position Cr of the rotor casing 12. That is, the pressure in the confined spaces at the axial position of the screw rotor is higher on the discharge side than on the suction side, and the twisted shape of the screw rotor causes the pressure in each tooth groove (each confined space) to differ even in a cross section at the same axial position. Due to the relationship between this difference in pressure between the tooth grooves and the support position of the screw rotor, the position where the bow-shaped deformation in the region where the screw rotor teeth are provided is greatest is a position shifted toward the discharge side from the axial center position of the region where the teeth are provided.

[0028] Therefore, according to the screw compressor 2 according to some embodiments, the relief surface 30 can be provided in the area where there is a high possibility of contact with the male rotor 15 and the female rotor 17.

[0029] In the screw compressor 2 according to some embodiments, as described above, the dividing plane Pd may coincide with the above-described imaginary plane Pv. This makes it easier to process the inner wall surfaces 12W of the first rotor casing 121 and the second rotor casing 122 compared to when the dividing plane Pd is deviated from the virtual plane Pv.

[0030] As a result of careful investigation by the inventors, it was found that when the rotor casing 12 is viewed from the axial direction, the position at which the amount of radially outward deformation when the male rotor 15 is deformed into a bow shape is greatest exists within a range Rm1 of up to 90 degrees from the above-mentioned imaginary plane Pv as the starting point in the direction opposite to the rotational direction of the male rotor 15, as indicated by arrow a, as shown in Figure 3. Furthermore, when the rotor casing 12 is viewed from the axial direction, it was found that the position at which the amount of radially outward deformation when the female rotor 17 is deformed into a bow shape is greatest exists within a range Rf1 of up to 90 degrees from the above-mentioned virtual plane Pv as the starting point in the direction opposite to the rotation direction of the female rotor 17, as indicated by arrow b.

[0031] Therefore, in the screw compressor 2 according to some embodiments, the clearance 30 on the inner wall surface 12W that faces the teeth of the male rotor 15 may be provided within the above-mentioned range Rm1. The clearance 30 on the inner wall surface 12W that faces the teeth of the female rotor 17 may be provided within the above-mentioned range Rf1. This allows the relief surfaces 30 to be provided in areas that are likely to come into contact with the male rotor 15 and the female rotor 17 .

[0032] 3, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 includes the entire range Rm1 and extends beyond the range Rm1 in the direction opposite the rotational direction of the male rotor 15, as indicated by arrow a. The flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 includes the entire range Rf1 and extends beyond the range Rf1 in the direction opposite the rotational direction of the female rotor 17, as indicated by arrow b. However, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be provided only in a portion of the range Rm1. Similarly, the flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be provided only in a portion of the range Rf1.

[0033] Furthermore, as a result of careful investigation by the inventors, it was found that when the rotor casing 12 is viewed from the axial direction, the circumferential position at which the amount of radially outward deformation when the male rotor 15 is deformed into a bow shape is greatest is the direction in which the radial load Fm acting on the male rotor 15 acts. Furthermore, when the rotor casing 12 is viewed from the axial direction, it was found that the circumferential position at which the amount of radially outward deformation of the female rotor 17 when it is deformed in a bow shape is greatest is the direction in which the radial load Ff acting on the female rotor 17 acts.

[0034] The magnitude and direction of the radial loads Fm and Ff generated in the radial bearing 18 are determined by the pressure distribution around the male rotor 15 and the female rotor 17. As shown in FIG. 3, four regions are roughly defined at different circumferential positions for each of the male rotor 15 and the female rotor 17, and the pressure in the enclosed space for each of these four regions will be described. The four regions at different circumferential positions on the male rotor 15 are designated as region cm1, region cm2, region cm3, and region cm4, in that order along the rotation direction of the male rotor 15 indicated by arrow a, starting from the region closest to the upper cusp 124. Similarly, the four regions with different circumferential positions on the female rotor 17 are designated as region cf1, region cf2, region cf3, and region cf4, in that order along the rotation direction of the female rotor 17 indicated by arrow b, starting from the region closest to the upper cusp 124.

[0035] As the male rotor 15 rotates, the pressure in the confined space in the male rotor 15 increases in the order of area cm1 → area cm2 → area cm3 → area cm4. Similarly, as the female rotor 17 rotates, the pressure in the confined space in the female rotor 17 increases in the order of area cf1 → area cf2 → area cf3 → area cf4. That is, the pressure in the confined space is highest around the lower cusp 125 around the discharge port 54, and the pressure in the confined space is lowest around the upper cusp 124. Due to this pressure difference, the radial load Fm acting on the male rotor 15 is directed diagonally upward and to the right as shown in FIG. 3, and the radial load Ff acting on the female rotor 17 is directed diagonally upward and to the left as shown in FIG.

[0036] Therefore, in the screw compressor 2 according to some embodiments, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be provided, when viewed from the axial direction, so as to include a range Rm2 of up to 35 degrees in both the direction of rotation of the male rotor 15 indicated by arrow a and the direction opposite to said rotational direction, with the direction of action of the radial load Fm acting on the male rotor 15 as its center. The flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be provided, when viewed from the axial direction, so as to include a range Rf2 of up to 35 degrees in both the direction of rotation of the female rotor 17 indicated by arrow b and the direction opposite to said rotational direction, with the direction of action of the radial load Ff acting on the female rotor 17 as its center. This allows the relief surfaces 30 to be provided in areas that are likely to come into contact with the male rotor 15 and the female rotor 17 .

[0037] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0038] The contents described in each of the above embodiments can be understood, for example, as follows. (1) The rotor casing 12 of the screw compressor 2 according to at least one embodiment of the present disclosure is a rotor casing 12 of the screw compressor 2 that houses a screw rotor (male rotor 15 and female rotor 17) including a pair of a male rotor 15 and a female rotor 17. The rotor casing 12 includes a first rotor casing 121 and a second rotor casing 122 that are divided by a dividing plane Pd that is parallel to an imaginary plane Pv that includes an imaginary central axis (central axis AX1) of the male rotor 15 and an imaginary central axis (central axis AX2) of the female rotor 17. The first rotor casing 121 and the second rotor casing 122 have inner wall surfaces 12W (compression section inner wall surfaces 12Wp) that form a confined space for compressing the gas to be compressed that is drawn through an intake port 52 on one axial side (intake side) of the screw rotors (male rotor 15 and female rotor 17). The second rotor casing 122 is in communication with a discharge port 54 on the other axial side (discharge side). In at least a portion of the axial region, the radius of curvature of the inner wall surface 12W (compression section inner wall surface 12Wp) of the first rotor casing 121 is larger than the radius of curvature of the inner wall surface 12W (compression section inner wall surface 12Wp) of the second rotor casing 122.

[0039] According to the above configuration (1), it is possible to reduce frictional resistance such as sliding loss between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17). Furthermore, according to the configuration (1) above, by making the radius of curvature of the inner wall surface 12W (compression section inner wall surface 12Wp) of the first rotor casing 121 larger than the radius of curvature of the inner wall surface 12W (compression section inner wall surface 12Wp) of the second rotor casing 122 in at least a portion of the axial region of the screw rotor (male rotor 15 and female rotor 17), undesired contact between the screw rotor (male rotor 15 and female rotor 17) and the inner wall surface 12W of the rotor casing 12 can be reduced. According to the configuration (1) above, the gap between the inner wall surface 12W of the second rotor casing 122, which closely contributes to the process of compressing the compressed gas, and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) can be made relatively small, thereby reducing leakage of the compressed gas from the gap. That is, according to the configuration (1) above, the gap between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) and the gap between the inner wall surface 12W of the second rotor casing 122 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) can be set individually, thereby reducing frictional resistance such as sliding loss and undesired contact between the screw rotors (male rotor 15 and female rotor 17) and the inner wall surface 12W of the rotor casing 12, while also reducing leakage of compressed gas from the gap between the inner wall surface 12W of the rotor casing 12 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17).

[0040] (2) In some embodiments, in the configuration of (1) above, a portion of inner wall surface 12W of first rotor casing 121 that is formed so as to have a larger radius of curvature than inner wall surface 12W of second rotor casing 122 in a partial axial region may have flank surface 30 defined by a curve when viewed in the axial direction. It is preferable that flank surface 30 be located radially outward of an imaginary cylindrical surface 25 whose radius is the radius of curvature of inner wall surface 12W of second rotor casing 122.

[0041] According to the above configuration (2), by providing the relief surface 30, undesired contact between the screw rotors (male rotor 15 and female rotor 17) and the inner wall surface 12W of the rotor casing 12 can be reduced.

[0042] (3) In some embodiments, in the configuration of (2) above, the relief surface 30 may be formed at a position shifted toward the discharge port 54 side (discharge side) from the axial center position Cr of the first rotor casing 121.

[0043] According to the above configuration (3), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0044] (4) In some embodiments, in any of the configurations (1) to (3) above, the dividing plane Pd may coincide with the virtual plane Pv.

[0045] According to the configuration (4) above, the inner wall surfaces 12W of the first rotor casing 121 and the second rotor casing 122 can be machined more easily than when the dividing plane Pd is deviated from the virtual plane Pv.

[0046] (5) In some embodiments, in any of the configurations (2) or (3) above, the flank 30 on the inner wall surface 12W that faces the teeth of the male rotor 15 may be located within a range Rm1 of up to 90 degrees from the imaginary plane Pv in the direction opposite to the rotational direction of the male rotor 15 when viewed from the axial direction. The flank 30 on the inner wall surface 12W that faces the teeth of the female rotor 17 may be located within a range Rf1 of up to 90 degrees from the imaginary plane Pv in the direction opposite to the rotational direction of the female rotor 17 when viewed from the axial direction.

[0047] According to the above configuration (5), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0048] (6) In some embodiments, in any of the configurations (2) or (3) above, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be provided, when viewed from the axial direction, to include a range Rm2 of up to 35 degrees in both the rotational direction of the male rotor 15 and the direction opposite to said rotational direction, with the direction of action of the radial load Fm acting on the male rotor 15 as its center. The flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be provided, when viewed from the axial direction, to include a range Rf2 of up to 35 degrees in both the rotational direction of the female rotor 17 and the direction opposite to said rotational direction, with the direction of action of the radial load Ff acting on the female rotor 17 as its center.

[0049] According to the above configuration (6), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0050] (7) The screw compressor 2 according to at least one embodiment of the present disclosure comprises a screw rotor (male rotor 15 and female rotor 17) including a pair of a male rotor 15 and a female rotor 17, and a rotor casing 12 of the screw compressor 2 having any of the configurations (1) to (6) above.

[0051] According to the above configuration (7), undesired contact between the screw rotors (the male rotor 15 and the female rotor 17) and the inner wall surface 12W of the rotor casing 12 can be reduced. Furthermore, according to the configuration (7) above, it is possible to reduce the sliding loss of oil existing between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17). According to the configuration (7) above, the gap between the inner wall surface 12W of the second rotor casing 122, which closely contributes to the process of compressing the gas to be compressed, and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) can be made relatively small, thereby reducing leakage of the gas to be compressed from the gap. That is, according to the configuration (7) above, the gap between the inner wall surface 12W of the first rotor casing 121 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) and the gap between the inner wall surface 12W of the second rotor casing 122 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17) can be set individually, thereby reducing undesired contact between the screw rotors (male rotor 15 and female rotor 17) and the inner wall surface 12W of the rotor casing 12 while reducing leakage of compressed gas from the gap between the inner wall surface 12W of the rotor casing 12 and the tooth tips of the screw rotors (male rotor 15 and female rotor 17). [Explanation of symbols]

[0052] 2. Screw compressor 12 rotor casing 12 12a Expanded diameter part 12e end 12W inner wall 12Wp Compression section inner wall 15 Male Rotor 17 Female rotor 18 Radial bearing 20 Thrust bearing 21 Suction side bearing housing 22 Discharge side bearing housing 30 Flank 31 areas 50 Suction space 52 Intake port 54 Discharge port 121 First rotor casing 122 Second rotor casing

Claims

1. A rotor casing for a screw compressor that houses a screw rotor including a pair of male and female rotors, the rotor casing includes a first rotor casing and a second rotor casing divided by a dividing plane parallel to an imaginary plane including an imaginary central axis of the male rotor and an imaginary central axis of the female rotor, the first rotor casing and the second rotor casing have inner wall surfaces that form a confined space for compressing the gas to be compressed that is sucked in through a suction port on one side in the axial direction of the screw rotor, the second rotor casing communicates with a discharge port on the other side in the axial direction, In at least a portion of the axial direction, the radius of curvature of the inner wall surface of the first rotor casing is larger than the radius of curvature of the inner wall surface of the second rotor casing. Rotor casing of a screw compressor.

2. a portion of the inner wall surface of the first rotor casing in a partial region in the axial direction that is formed so as to have a larger radius of curvature than the inner wall surface of the second rotor casing has a relief surface that is defined by a curve when viewed from the axial direction, the relief surface is located radially outward of an imaginary cylindrical surface having a radius equal to the radius of curvature of the inner wall surface of the second rotor casing.

2. A rotor casing for a screw compressor according to claim 1.

3. the relief surface is formed at a position shifted toward the discharge port from a center position in the axial direction of the first rotor casing.

3. A rotor casing for a screw compressor according to claim 2.

4. The dividing surface coincides with the virtual plane. A rotor casing for a screw compressor according to any one of claims 1 to 3.

5. the relief surface on the inner wall surface facing the teeth of the male rotor is provided within a range of up to 90 degrees from the imaginary plane as a starting point in a direction opposite to the rotation direction of the male rotor when viewed from the axial direction, the relief surface on the inner wall surface facing the teeth of the female rotor is provided within a range of up to 90 degrees from the imaginary plane as a starting point in a direction opposite to the rotation direction of the female rotor when viewed from the axial direction.

4. A rotor casing for a screw compressor according to claim 2 or 3.

6. the relief surface on the inner wall surface facing the teeth of the male rotor is provided, when viewed from the axial direction, to include a range of up to 35 degrees in both the rotational direction of the male rotor and the direction opposite to the rotational direction, with the direction of action of a radial load acting on the male rotor as the center; the relief surface on the inner wall surface facing the teeth of the female rotor is provided so as to include a range of up to 35 degrees in both the rotational direction of the female rotor and the direction opposite to the rotational direction, with the direction of action of a radial load acting on the female rotor as the center, when viewed from the axial direction.

4. A rotor casing for a screw compressor according to claim 2 or 3.

7. a screw rotor including a pair of male and female rotors; A rotor casing for a screw compressor according to any one of claims 1 to 3; A screw compressor comprising:

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